It has been 36 years since 15-year-old Elizabeth Eckford walked a gauntlet of jeering whites to attend Central High School in Little Rock, Ark., and 31 years since James Meredith became the first black student at the University of Mississippi. Today, the mobs and the protective soldiers are gone, but hopes that public school integration would lead to an inclusive atmosphere at colleges and universities have been battered by the reality of racial and ethnic tensions at campuses across the country. Indeed, the nationwide push for integration appears to have reached a turning point, an outgrowth of the nation's lingering legacy of segregated housing. Now some researchers are even questioning whether integration has a positive effect on black children's academic and social development.